Gas turbines, which may also be referred to as combustion turbines, are internal combustion engines that accelerate gases, forcing the gases into a combustion chamber where heat is added to increase the volume of the gases. The expanded gases are then directed towards a turbine to extract the energy generated by the expanded gases. Gas turbines have many practical applications, including use as jet engines and in industrial power generation systems.
Among the components of a gas turbine may be one or more nozzles that may direct and accelerate a flow of gases toward turbine blades (may also be referred to as “buckets”) to cause the blades to rotate about an axis at the center of the gas turbine. Such nozzles may be stationary and in the form of an airfoil that extends radially between an outer endwall and inner endwall of a gas turbine. Hot gases may flow through a path that is formed by the outer and inner endwalls and the airfoil walls. A leading edge of each endwall may form an overhang that extends upstream from each such airfoil. As will be appreciated, this leading edge and the endwalls can reach very high temperatures, and overheating may affect turbine performance. Therefore, measures are often taken to cool these sections of a gas turbine. While the central portion of the endwall can be cooled by impingement, the leading edge portion of a nozzle airfoil endwall may overlap portions of a turbine blade by design (e.g., a turbine blade “angel wing”) in order to prevent gases from flowing through the space under the leading edge. This leading edge overhang configuration of a nozzle endwall may be particularly difficult to cool. This portion may also be subject to particularly high temperatures and stresses as the blade portions directly proximate to the leading edge portion of a nozzle airfoil may on occasion rub the leading edge. An impingement plate design is not well suited to cool this portion as it will not typically be robust enough to endure contact between the blade and the nozzle airfoil endwall.